BER Distribution – evaluation of error distribution against different factors (position on the track, error length, written bit sequence, and read bit sequence)

BER Performance – production test, which measures on-track BER and the track width for the given BER thresholds for different position of the adjacent track

BER 747A Test

The BER 747A test is an engineering tool to evaluate BER degradation with writing of the adjacent track. The test allows you to specify up to five thresholds for the 747 plot and evaluate bathtub variation versus position of the adjacent tracks.

Depending on parameters, the test can perform single read-only BER measurement at a given offset from the track center, or complete sequence of band erase, writing side tracks, writing the signal track, writing the adjacent tracks sweeping position, building bathtub curve, and calculating results.

The test provides numeric results, stores all measured data in a file using the CSV format, and shows the following three plots:

Figure 3: BER Versus Adjacent Track

BER Linear Density Test

For frequencies in the specified range, the test performs a band erase, writes the side tracks, writes the signal track, writes the adjacent track in the single position, and measures BER. The test either measures one BER value for single offset, or it builds the bathtub curve for multiple offsets in the specified range. The test performs PRML channel optimization periodically to achieve the best BER for each data rate.

The test provides numeric results, stores all measured data in a file using CSV format, and shows the following two plots:

Bathtub Plot – A family of BER graphs versus the read head position for different frequencies

Off-Track BER Plot – A family of BER graphs at a given offset versus signal frequency

The purpose of the test is to determine the optimum data rate (linear density) for the head, media, and PRML channel combination.

Figure 4: BER Roll-off Curve Versus Frequency

Figure 5: BER Versus Reader Position

BER Distribution

The BER Distribution Test examines the distribution of errors detected by PRML channel versus four parameters and provides the following plots:

Error Length Plot – Number of errors of defined error length

Sector Number Plot – Error distribution across a revolution

Written Byte Plot – Number of errors, which occurred during writing a particular byte of the user data pattern

Read Byte Plot – Number of errors during reading a particular value back from the media

The first plot allows predicting the error rate after applying the user error-correction algorithm. The second helps to detect sectors having defects for the selected track and exclude them from the subsequent testing. The third and the fourth show the encoding scheme performance in the PRML channel.

Figure 6: Error Distribution Versus Error Length

BER Performance

The BER Performance Test is a test designed for using in production. The test measures the best bit error rate and track width for the given level of BER for three track preconditions:

Track on Erased Media – perform band erase, write a signal track and perform the measurement

Track on Prewritten Media – perform band erase, write side tracks, write a signal track and perform the measurement